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Molecular organization and dynamics in bacteriorhodopsin-rich reconstituted membranes: discrimination of lipid environments by the oxygen transport parameter using a pulse ESR spin-labeling technique. Biochemistry 1994 Apr 26;33(16):4947-52

Date

04/26/1994

Pubmed ID

8161556

DOI

10.1021/bi00182a025

Abstract

Molecular organization and dynamics in protein-rich membranes have been studied by investigating transport (diffusion-concentration product) of molecular oxygen at various locations in reconstituted membranes of bacteriorhodopsin (BR) and L-alpha-dimyristoylphosphatidylcholine. Oxygen transport was evaluated by monitoring the bimolecular collision of molecular oxygen with four types of nitroxide lipid spin labels placed at various locations in the membrane. The collision rate was estimated from the spin-lattice relaxation times (T1's) measured at various oxygen partial pressures by analyzing the short-pulse saturation recovery ESR signals. CD spectra and decay of polarized flash-induced photodichroism of bacteriorhodopsin indicated that BR molecules are monomers in reconstituted membranes with a lipid/BR molar ratio of 80 (80-rec) and are 25% monomers and 75% trimers plus oligomers of trimers when the lipid/BR ratio is 40 (40-rec). In the 80-rec, the lipid environment is homogeneous on a microsecond scale (T1), probably because the exchange rate of lipids between the bulk and the boundary regions is greater than the T1 relaxation rate (approximately 10(6) s-1). The oxygen collision rate in the hydrophobic region of the 80-rec membrane is smaller by a factor of 1.6 than in that of the lipid membrane without BR, and the effect of BR in decreasing the collision rate is independent of the "depth" in the hydrophobic region. In the 40-rec, two collision rates were observed, one of which is close to those for purple membrane (or the gel-phase membrane), while the other is about the same as was measured in the 80-rec.(ABSTRACT TRUNCATED AT 250 WORDS)

Author List

Ashikawa I, Yin JJ, Subczynski WK, Kouyama T, Hyde JS, Kusumi A

Author

Witold K. Subczynski PhD Professor in the Biophysics department at Medical College of Wisconsin




MESH terms used to index this publication - Major topics in bold

Bacteriorhodopsins
Circular Dichroism
Diffusion
Dimyristoylphosphatidylcholine
Electron Spin Resonance Spectroscopy
Membrane Lipids
Membrane Proteins
Models, Chemical
Nitrogen Oxides
Oxygen
Spin Labels